In dental surgery, the conventional solution is to use a syringe to inject a determined quantity of liquid anesthetic into the gum of the patient at a certain distance from the tooth that is to be attended to. However, that procedure suffers from drawbacks such as a considerable latency time between injection and anesthetic action, and of a quantity of anesthetic being injected that is larger than necessary. To remedy those drawbacks, proposals have already been made to provide intradiploic anesthesia whereby injection takes place directly into the marrow of the maxillary bone after passing through the cortical substance. The action of the anesthetic is thus more effective. To this effect, it is known to cause the injection needle to rotate so as to facilitate penetration of the needle through the cortical substance which is a hard region. After which a piston is displaced which bears against the moving end of the cartridge containing the anesthetic.
Proposals have already been made, in particular in U.S. Pat. No. 5,173,050 to perform such anesthesia in two stages. Initially the cortical substance is pierced, after which the injector is withdrawn and the perforation needle is replaced by an injection needle. However it is very difficult to find the perforation again so as to proceed with injection.
An injector that enables such anesthesia to be performed without needing to remove the perforation needle is described in FR-A-2 581 548. In that patent, the means for rotating the cartridge and for moving the moving end of the cartridge are constituted by two micro-motors, with the mechanical link between the cartridge and the motor for rotating said cartridge being obtained by means of gears. The same applies to driving the piston which is obtained via stepdown gearing. It is thus possible to obtain injection that is continuous and regular, which was not the case with hand syringes. However, it turns out that those drives give rise to undesirable noise, since the motor is rotating at very high speeds of several tens of thousands of revolutions per minute.